Field of the Invention
The present invention relates to a radiation tomography device having a radiation source and a radiation detector, and particularly relates to a technology by which a positional range of the radiation detector, which enables imaging of the radiation tomography image, is automatically calculated.
Description of the Related Art
In medical fields, a radiation imaging device based on an imaging technology so-called tomosynthesis, which is a device to obtain a tomographic image of a cross section of a subject by utilizing a radiation, has been used (Patent Document 1, 2.) As for such radiation tomographic device, a radiation source and a radiation detector are in place facing each other as if sandwiching the subject. When imaging a series of radiation images, the radiation source is being moved relative to the radiation detector. Then, a radiation tomographic image of the subject is reconstructed based on the obtained series of radiation images by a digital processing and then is displayed on a display element e.g., a monitor. In addition, a flat panel display (FPD) is primarily used for the radiation detector.
Referring to FIG. 20A, 20B, the inventor set forth the structure of a conventional radiation tomographic imaging device. The conventional radiation tomography 100 includes a support post 101, a radiation source 103, a FPD 105 and a moving mechanism 107. The radiation source 103 is installed to the support post, which is based on the ceiling of the examination room, to be movable freely.
Further, as indicated by the arrow referring to FIG. 20A, the radiation source 103 intermittently irradiates from the position indicated by the solid line to the position indicated by the broken line, in a y-direction, i.e., while moving to the body axis of the subject M, the radiation is intermittently irradiated to the subject M from the focus point 103a relative to the subject M. The FPD 105 detects the radiation irradiated from the focus point 103a and passed through the subject M, and output as a radiation detection signal. And the radiation image of the subject M is generated based on the detection signal output from the FPD 105.
The moving mechanism 107 controls the movement of the radiation source 103 in the y-direction and also tilts the radiation source 103 relative to the y-direction so that the center axis 103b of the radiation beam irradiated from the focus point 103a can always pass the center point P of the detection face of the FPD 105. The radiation source 103 changes sequentially an irradiation angle of the radiation interlockingly with the moving direction of the radiation source 103 in the y-direction, so that the radiation source 103 can constantly irradiate the center point P. In addition, a height from a floor surface W to the center point of the detection face of the FPD 105 is F.
Specifically, the radiation source 103 irradiates sequentially the radiation while sequentially changing the swing angle thereof, so that a number of radiation images due to the different incident angles relative to the target region can be generated. The number of acquired radiation images is reconstructed so that the radiation tomography images of the subject M of the expected cross sections can be obtained.
Referring to FIG. 20B, according to the conventional radiation tomography device 100, the moving mechanism 107 may move synchronously the radiation source 103 and the FPD 105. Specifically, the moving mechanism 107 moves the radiation source 103 and the FPD 105 and reversely each other in the y-direction so that the central axis 103b of the X-ray beam can pass the cross section center Q that is a target region. Thus, the radiation source 103 and the FPD 105 move in the opposite direction each other sandwiching the subject M while keeping the positions facing each other. In such case, a radiation image relative to the base cross section Ma including the cross section center Q and parallel to the detection face can be generated.
An enlargement factor of the acquired radiation tomography image is affected by the distance between the focus point 103a and the detection face (imaging distance) and a cross section thickness of the radiation tomography image is affected by the swing angle (irradiation swing angle) of the radiation source while intermittently irradiating the radiation. It is desired that if the enlargement factor should be smaller, the imaging distance, referring to FIG. 20A, FIG. 20B, should be longer. Further, it is desired that if the cross section thickness should be thinner, the irradiation swing angle θ should be larger.